Device for regulating the speed of electric motors



April 1940- KARL-GUSTAV ALLSTROM 6,434

mzvrca m aneuusrme THE swan OF ELECTRIC MOTORS Filed Dec. 23, 1937 2Sheets-Sheet 1 INVENTOR KA RL- GUSTAV ALLSTROM I BY ATTORNEY.

April 9, 1940- KARL-GUSTAV ALLSTROM 34 DEVICE FOR REGULATING THE SPEEDOF ELECTRIC MOTORS 2 Sheets- Sheet 2 Filed Dec. 23, 1937 Jnveniar: I IKarl-@ur/av #[Lrfro'm 7 Patented Apr. 9, 1940 UNITED STATES DEVICE FORREGULATING THE SPEED OF ELECTRIC MOTORS Karl-Gustav Allstriim, Uster,Switzerland Application December 23, 1937, Serial No. 181,360 In GermanyDecember 30, 1936 2 Claims. (Cl. 171-221 This invention relates to adevice for regulating the speed and maintaining constant the actuallyadjusted number of revolutions of small electric motors.

e In the driving motors for talking machines adjusting devices are knownin which an adjustable centrifugal governor and a series resistance areemployed. When using repulsion motors the regulation of the number ofrevolutions is efiected by a brush adjustment instead of a resistance,adjustment. The known arrangements are sufficient for talking machinemotor drives, owing to the relatively small fluctuations in load andowing to the relatively small range of adjustment required. However,these known de vices are not sufficient for the fluctuations in loadoccurring in the driveof sewing machines and the wide range ofadjustments necessary for carrying out the different kinds of sewingwork.

According to the invention the adjusting element of the centrifugalbrake governor is connected with an adjusting element of the seriesresistance or brush device. It is thus possible for the seamstress byoperating a single adjusting element to switch on the motor, adjust tothe desired speed, to change over slowly or suddenly from the actuallyadjusted speed to a higher or lower speed, and finally, by a simplemanipulation of this adjusting element to switch of! the motor and tobrake immediately. Consequently with the motor adjustment according tothe invention it is possible to carry out all fine sewing machine workwhich hitherto could only be carried out with hand drive or pedal drive.

It has been found by experiment, that in practice a centrifugaladjustment is only necessary within the lower speed range, whereas thecentrifugal adjustment can be dispensed with at high speeds.

Two embodiments of the invention are illustrated by way of example inthe accompanying drawings, in which: I

Fig. 1 shows a speed regulating device partly in elevation, partlyin-section,

Fig. 2 shows a modified form of construction partly in elevation, andpartly in section,

Fig. 3 is an end elevation viewed from the right of Fig. 2.

A motor I, in the example illustrated a series collector motor, drives,for example, a sewing machine by a belt from a grooved pulley. Acylindrical extension of the motor housing is constructed as guidecasing 3 surrounding a centrifugal brake governor. A sleeve 5 is fixed,for example pinned, on the end of the motor shaft 4.

A brake disc 6, whose hub has a keyway i in which a key engages isslidable on the shaft .4. Arms II and iii are pivotally mounted at oneend at 8 in the sleeve Sand at 9 in the brake disc 6 respectively and atthe other ends at I; 5 and I2 respectively in fly balls I. A pressurespring i5 presses the brake disc 6 towards the motor, thereby extendingthe arms I0 and it so that they and the fiy balls i4 assume the positionshown in the drawings. The guide casing 3 has 10 an arm IS, on which acontrol lever I8 provided with slot 19 is oscillatably mounted at ll. Adrum-shaped brake block 20 is arranged in the guide casing 3 slidable inthe axial direction of the motor, This block has a projection I! carry-5 ing a pin 22 which engages in the slot I! in the control lever l8.

Current is supplied to the motor by wires 23 and 24. The wire isconnected to one terminal 25 of the motor I, whereas the wire 24 isconnected to a contact arm 28 of a series resistance 29,diagrammatically shown in the drawings. A wire 30 extends from one endof the resistance 29 to the other terminal.26 of the motor. The contactarm 28 is pivoted at 21 on a lever 3|, the 25 free end of which lever isconnected by a rod 32 with the control lever IS.

The device operates in the following manner:

For starting the motor the control lever [B is swung in the direction ofthe arrow A until the contact arm 28 reaches the contact path of theresistance 29. At the same time the brake block 20 is shifted slightlyin outward direction. When the motor has attained a certain speed, theflyballs l4 swing outwards pressing the brake disc 6 against the brakeblock 20 through the intermediary of the arms I0 and ii. The frictionbetween brake disc and brake block reduces the number of revolutions sothat it does not attain the value which would correspond to the actualload and size of the series resistance. If the control lever i8 is swungfurther in the direction of the arrow A, the brake block 20 is shiftedfurther towards the right away from the disc 6. Consequently the numberof revolutions increases, 5 the governor swings out farther until thebrake disc 6 again bears against the brake block 20.

If, when the motor is under a certain load, a certain number ofrevolutions has been adjusted by means of the control lever i8, and ifthe load on the motor decreases, the number of revolutions andconsequently the pressure and the friction between brake disc and brakeblock will increase until the reduction of load is compensated.

If, on the other hand, the load on the motor inu creases, the number ofrevolutions begins to drop with the result that the pressure andconsequently the friction between the brake disc and brake block willbecome less and the increase in load is compensated. It has been foundin practice, that fluctuations in load result in such slight alterationsof the speed actually adjusted that this may be regarded as almostconstant.

Figs. 2 and 3 show a repulsion motor with a regulating device mountedthereon. Brushes, of which the brush 3 is visible on the drawing, bearagainst the collector 33. The brush holders are mounted on the brushgear 36 which is easily rotatable in the housing of the motor Iconcentric with the shaft 1. A catch pin 38 radially mounted on thebrush carrier ring projects through a slot 31 in the housing wall and isengaged by a forked arm of the two-armed lever 39 oscillatably mountedon a pin on the housing wall. A connecting rod 32a connects the otherarm of the lever 39 to the control lever i8.

This device operates in a similar manner to that described in connectionwith the series motor already described. In the case of the series motorthe resistance 29 is switched on and of! with the aid of the, connectingrod 32 when the control lever i8 is operated whereas in the case of therepulsion motor the two-armed lever 39 is oscillated through theintermediary oi the connecting rod 320. and transmits the movement tothe brush carrier ring 36 through the intermediary oi the catch pin 38and thus effects a shifting oi the brushes 34 on the periphery of thecollector 33. This brush displacement then influences the current takenup or the speed of the motor in known manner.

I claim:

1. A device for regulating the speed and maintaining constant theactually adjusted number of revolutions of small electric motors,comprising in combination means for changing the speed of the motorhaving an adjusting element, an

adjustable centrifugal brake governor driven by the motor shaft andcarrying an adjusting element, and a linkage connecting the adjustingelement of said speed changing means with the adjusting element of saidgovernor.

2. A device as specified in claim 1, in which the motor is a repulsionmotor with shiftable brush holder said holder forming the means 'torchanging the speed of the motor.

KARL-GUSTAV AmsTRoM.

